[论文解读] Numerical investigation of high-pressure combustion in rocket engines using Flamelet/Progress-variable models

Alessandro Coclite, Luigi Cutrone+2 more|arXiv (Cornell University)|Dec 2, 2014

Combustion and flame dynamics参考文献 23被引用 3

一句话总结

该论文提出了一种用于高压氢/液氧火箭燃烧的新型火焰片/进度变量（FPV）模型，采用统计上最可能分布（SMLD）框架，消除了对混合分数与进度变量联合概率密度函数（PDF）的假设。通过整合真实气体状态方程（Peng-Robinson）和详细反应机理，该模型提高了火焰结构与温度的预测精度，特别是在喷注器附近，相较于传统FPV模型，在MASCOTTE V03实验案例中更准确地捕捉了火焰长度、厚度以及涡流卷吸效应。

ABSTRACT

The present paper deals with the numerical study of high pressure LOx/H2 or LOx/hydrocarbon combustion for propulsion systems. The present research effort is driven by the continued interest in achieving low cost, reliable access to space and more recently, by the renewed interest in hypersonic transportation systems capable of reducing time-to-destination. Moreover, combustion at high pressure has been assumed as a key issue to achieve better propulsive performance and lower environmental impact, as long as the replacement of hydrogen with a hydrocarbon, to reduce the costs related to ground operations and increase flexibility. The current work provides a model for the numerical simulation of high- pressure turbulent combustion employing detailed chemistry description, embedded in a RANS equations solver with a Low Reynolds number k-omega turbulence model. The model used to study such a combustion phenomenon is an extension of the standard flamelet-progress-variable (FPV) turbulent combustion model combined with a Reynolds Averaged Navier-Stokes equation Solver (RANS). In the FPV model, all of the thermo-chemical quantities are evaluated by evolving the mixture fraction Z and a progress variable C. When using a turbulence model in conjunction with FPV model, a probability density function (PDF) is required to evaluate statistical averages of chemical quantities. The choice of such PDF must be a compromise between computational costs and accuracy level. State- of-the-art FPV models are built presuming the functional shape of the joint PDF of Z and C in order to evaluate Favre-averages of thermodynamic quantities. The model here proposed evaluates the most probable joint distribution of Z and C without any assumption on their behavior.

研究动机与目标

• 开发适用于高压火箭发动机，特别是超临界条件下的更精确湍流燃烧模型。
• 通过引入统计上最可能分布（SMLD）框架，减少火焰片/进度变量（FPV）模型中对PDF形状的假设依赖。
• 评估真实气体效应与详细动力学机制对高压氢/液氧系统燃烧预测精度的影响。
• 基于MASCOTTE V03实验案例，评估所提模型的性能表现。

提出的方法

• 采用雷诺平均纳维-斯托克斯（RANS）求解器，结合低雷诺数k-ω湍流模型，模拟高压湍流流动。
• 采用火焰片/进度变量（FPV）模型，通过混合分数（Z）与进度变量（C）追踪热化学量。
• 应用SMLD框架计算Z与C的最可能联合分布，无需假设PDF的函数形式，从而提升统计精度。
• 引入Peng-Robinson状态方程以考虑超临界压力下的真实气体效应，这对密度与输运性质建模至关重要。
• 采用四种动力学机理——两种简化机理（Li与Warnatz）和两种详细机理（Li与Warnatz），以评估化学机理选择的影响。
• 基于MASCOTTE V03实验案例的实验数据对模型进行验证，重点关注温度与OH质量分数分布。

实验结果

研究问题

• RQ1 与假设PDF形状的传统FPV模型相比，基于SMLD的FPV模型在预测精度方面有何提升？
• RQ2 真实气体效应在高压氢/液氧火箭发动机中对火焰结构与燃烧效率的影响程度如何？
• RQ3 不同动力学机理（简化与详细）对点火延迟、火焰长度与反应区厚度预测的影响如何？
• RQ4 所提出的模型能否准确捕捉复杂流动特征，如角落涡卷吸与火焰前缘形变？

主要发现

• 基于SMLD框架的模型B相比模型A预测出更短且更符合实际的火焰长度，与实验数据吻合度更高。
• SMLD模型更准确地捕捉了由于角落涡卷吸引起的火焰前缘凸起特征，尤其在喷注器附近（x ≤ 0.03 m）。
• 在初始区域，模型B的火焰厚度增长更缓慢，正确反映了靠近冷液氧核心的薄而高温的热层。
• 详细Li机理相比简化机理能更准确预测温度与火焰结构，后者则高估燃烧速度并低估点火延迟。
• 结合SMLD框架与真实气体效应的模型显著提升了温度与OH质量分数分布的预测精度，尤其在喷注器下游前0.1 m范围内。
• 详细动力学、真实气体效应与基于SMLD的PDF建模三者结合，显著提升了高压燃烧模拟的保真度。